Magnetic bubble memories are well known in the art. One mode of operating such memories is called a field access mode as is also well known. A field access mode bubble memory is characterized by a magnetic field reorienting, typically rotating, in the plane of bubble movement. Bubbles, in response to the cyclical changes in the magnetic field move along paths defined by magnetically soft elements such as permalloy or, more recently, by a repetitive pattern of ion-implanted regions.
The most attractive organization for a field access bubble memory is called the major-minor organization. This organization includes a plurality of closed-loop paths, termed minor loops, and a single major path. A bubble generator and a bubble detector are associated with the major path in spaced-apart positions operative to produce a bubble pattern in the major path and to detect such a pattern respectively.
Movement in all the paths is produced by the rotating magnetic field. Bubble movements in the minor loops and the major path thus are synchronous. Accordingly, bubble movement between the minor loops and the major path is achieved by the generation of appropriate magnetic control fields during a selected cycle of the magnetic field.
Commonly, the control fields are generated at the ends of the minor loops where those loops come into close proximity with the major path. At those ends, the geometries of the ion-implanted regions, for example, are different and an electrical conductor is coupled to the layer of bubble movement at the positions of close proximity so that bubbles can be moved between the minor loops and the major path by a pulse on the conductor during a selected cycle.
Frequently, a separate conductor couples positions of close proximity between minor loops and the major path at each set of ends of the minor loops. The elements and conductors at one set of ends are adapted to transfer bubble patterns into the minor loops; those at the other set of ends being adapted to transfer bubble patterns out of the minor loops. It can be seen that bubbles from the generator are organized in the major path for transfer into the minor loops for permanent storage while bubbles permanently stored in the minor loops are transferred out to the major loop for detection all in response to the rotating magnetic field and appropriately timed transfer-in and transfer-out pulses.
If transfer-out and transfer-in operations result in the movement of bubble patterns into and out of a single major path coupled to opposite ends of the minor loops, an inversion of the bubble pattern occurs. That is to say, the pattern transferred out at one end of the minor loops is inverted from the one transferred back in. This problem is overcome by the use of a G-shaped major path or loop as disclosed in copending application Ser. No. 018,310 filed for T. M. Burford, Mar. 7, 1979. The G-shaped organization introduces a compensating inversion of the bubble pattern.
If the G-shaped organization is implemented by ion implantation, either the transfer-out operation or the transfer-in operation is implemented in a manner to result in the movement of a bubble pattern between the minor loops and an auxiliary propagation path not opposed to the ends of the minor loops. That is to say transferred bubbles are moved to or from an auxiliary propagation path separated from the minor loops by a nonimplanted region. If the auxiliary path occurs at the transfer-out end of the minor loops as in the above-mentioned Burford application, for example, a merger of the auxiliary path and the major loop is desirable to avoid recirculation of data through the transfer-out region. An ion-implanted merge port is required at this juncture. The problem thus, is to provide an ion-implanted magnetic bubble memory with a passive merge port allowing bubbles from one of two paths to advance along a single path in an ion-implanted bubble memory.